MEMORY(2) MEMORY(2) NAME memccpy, memchr, memcmp, memcpy, memmove, memset, tsmemcmp - memory operations SYNOPSIS #include <u.h> #include <libc.h> void* memccpy(void *s1, void *s2, int c, usize n) void* memchr(void *s, int c, usize n) int memcmp(void *s1, void *s2, usize n) void* memcpy(void *s1, void *s2, usize n) void* memmove(void *s1, void *s2, usize n) void* memset(void *s, int c, usize n) #include <libsec.h> int tsmemcmp(void *s1, void *s2, ulong n) DESCRIPTION These functions operate efficiently on memory areas (arrays of bytes bounded by a count, not terminated by a zero byte). They do not check for the overflow of any receiving memory area. Memccpy copies bytes from memory area s2 into s1, stopping after the first occurrence of byte c has been copied, or after n bytes have been copied, whichever comes first. It returns a pointer to the byte after the copy of c in s1, or zero if c was not found in the first n bytes of s2. Memchr returns a pointer to the first occurrence of byte c in the first n bytes of memory area s, or zero if c does not occur. Memcmp compares its arguments, looking at the first n bytes only, and returns an integer less than, equal to, or greater than 0, according as s1 is lexicographically less than, equal to, or greater than s2. The comparison is bytewise unsigned. Memcpy copies n bytes from memory area s2 to s1. It returns s1. Memmove works like memcpy, except that it is guaranteed to MEMORY(2) MEMORY(2) work if s1 and s2 overlap. Memset sets the first n bytes in memory area s to the value of byte c. It returns s. Tsmemcmp is a variant of memcmp that is safe against timing attacks. It does not stop when it sees a difference, this way it's runtime is function of n and not something that can lead clues to attackers. SOURCE All these routines have portable C implementations in /sys/src/libc/port. Most also have machine-dependent assem- bly language implementations in /sys/src/libc/$objtype. Tsmemcmp is found on /sys/src/libsec/port/tsmemcmp.c. SEE ALSO strcat(2) BUGS ANSI C does not require memcpy to handle overlapping source and destination; on Plan 9, it does, so memmove and memcpy behave identically. If memcpy and memmove are handed a negative count, they abort. Memcmp should not be used to compare sensitive data as it's vulnerable to timing attacks. Instead, tsmemcmp should be used.